1. Field of the Invention
The present invention relates generally to a method and apparatus for the degasification of a gas-laden fluid and, more particularly, to such a method and apparatus for use with drilling mud compositions.
2. Description of the Prior Art
It is often desirable in various industrial operations to substantially remove gas from a fluid being processed. A prime example of this is in the oil well drilling industry where it is customary to pump substantial quantities of a specially formulated drilling mud down through the drill stem to be discharged through apertures adjacent the drill bit. Not only does the drilling mud lubricate the drill bit and remove the cuttings therefrom, but the weight of the column of drilling mud in the drill stem prevents the escape or blowout of natural gas formations encountered by the drill. However, the drilling mud, in this latter capacity, frequently becomes contaminated in the well with natural gas or air which decreases its weight and viscosity, thus markedly diminishing its effectiveness in preventing blowouts. Since it is uneconomical to continuously supply fresh, uncontaminated drilling mud to the well, it is necessary that the mud be recycled and that the entrained gases therein be removed before the mud is reused in the well.
Numerous prior art systems have been proposed for degassing drilling muds. These systems characteristically utilize a vacuum tank having some sort of baffle structure over which the mud flows in a thin film; the vacuum in the tank causes the gas to escape from the thin film of mud. For example, the applicant's own prior U.S. Pat. No. Re. 27,882 shows such a vacuum tank structure and further discloses separating the liberated gas from the mud in a cyclone separator. Similarly, U.S. Pat. Nos. 580,169 to Washington and 3,229,449 to Hogue show other types of vacuum degassing apparatus. In Washington, supra, the vacuum separator includes an expanding-pipe section having a plurality of upwardly extending ridges which create eddies in the flow of the fluid therethrough, the eddies allowing the gas to be easily withdrawn from the fluid by the vacuum in the pipe. A disadvantage, however, of all such vacuum type drilling mud degassers is the need to generate and maintain a suitable source of vacuum and the need for large, complex baffle structures to spread the mud out into sufficiently thin layers to enable complete degasification thereof.
U.S. Pat. No. 3,769,779 to Liljestrand discloses another type of drilling mud degasser which operates at atmospheric pressure thereby obviating the need for a vacuum system. In Liljestrand (FIGS. 9 and 10), a radial-flow centrifugal pump is disposed below the level of the gas-laden mud held in a mud receiving tank. An upwardly extending vertical conduit connects the centrifugal pump to a gas separator with the outlet of the conduit being opposed by a planar surface. In the operation of Liljestrand's degasser, the centrifugal pump radially thrusts mud from the tank outwardly into the conduit with substantial force such that the mud exiting from the conduit strikes the planar surface and is laterally directed outwardly therefrom in tiny droplets to impinge on the surfaces of the separator. Because the mud is thrown against these surfaces at such high velocity, the gas therein is liberated and may be vented through an outlet while the degassed mud flows downwardly to a degassed mud receiving tank. A disadvantage of the Liljestrand apparatus, however, is the need for a relatively large horsepower centrifugal pump to impart the necessary force to the mud so that the degassing operation takes place properly. Similarly, degassing devices are known which utilize large horsepower jet-type pumps for imparting the necessary flow to the gas-laden drilling mud.